1. Field of Invention
This invention relates to low-firing, high durability glass and enamel compositions. In particular, the invention relates to glass frit compositions, and the glasses, ceramics and enamels made therefrom, which include ZnO, SiO2, B2O3 and TiO2. The glasses have good acid resistance, low CTE (<100×10−7) and relatively low firing temperatures (<1100° F.). All of this is achieved without the use of lead or bismuth.
2. Description of Related Art
Glass enamel compositions are well known in the art. One aim of conventional glass and enamel compositions is the achievement of a low firing, high durability glass and enamel having a low coefficient of thermal expansion (CTE). However, such glasses typically require the use of substantial amounts of relatively expensive Bi2O3.
Partially crystallizing glass enamel compositions that fuse at relatively low temperatures are used, for example, to form opaque dark-colored enamel bands on the outer edges of sections of automotive glass such as windshields and side and rear windows. These opaque dark-colored enamel bands, which typically vary in width from about 1.5 cm to about 15.0 cm, greatly enhance the aesthetic appearance of the sections of glass upon which they are applied and also block the transmission of sunlight through the glass to protect underlying adhesives from degradation by ultraviolet radiation. Moreover, these opaque colored enamel bands preferably have the ability to conceal silver-containing buss bars and wiring connections of rear glass defrosting systems from view from the outside of the vehicle.
Specially formulated glass enamel compositions can be applied to planar sections of glass and fired to form opaque dark-colored enamel bands at the same time as the bending or forming operations were performed on the section of glass. Such glass enamel compositions can fuse and partially crystallize at the temperature at which a section of glass would be preheated preparatory to a bending or forming operation. It is believed that the partial crystallization of the enamel forms a dense, hard, protective layer that prevents the enamel from sticking to the press or vacuum head during the glass bending and transporting operations.
Although improvements have been made in recent years, the chemical durability of known lead-free and cadmium-free glass enamel systems used in tableware, decorative ware, and automotive glass applications has been less than desired. Further, the presence of bismuth, an increasingly expensive metal, has been required in such formulations as a lead replacement. Therefore, a need exists for lead-free and cadmium-free (and preferably bismuth-free) enamel compositions that exhibit excellent chemical durability to acids, water, and alkalis. Such enamel compositions must be able to fuse and preferably, partially crystallize at temperatures at which sections of glass are preheated preparatory to forming operations so as not to stick to press or vacuum heads. Moreover, such enamel compositions should be effective in blocking ultraviolet radiation and in retarding the migration of silver and subsequent showing from overprinted buss bars and wiring connections of rear glass defrosting systems.